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LED Anode Voltage for ADPD1081



		

			

									
						jpetras
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Dec 14, 2021 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hi all,


Can we safely use a higher *anode* voltage on the LED than the 3.6Vmax listed for LEDXx? Does pin have protection that would allow this? My concern is not when the LED is being driven (LED Vf would be in play). Rather, when the LED is not being driven. I am concerned that the LED cathode voltage will float upward (albeit, very, very slowly), eventually clipping above 3.6V and putting stress on the pin. Do you have protection diodes in place in the pin?


Thank you!


Jason

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	

		
	











	

	

					



			


				
	









	
    
	

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                                 Analog Employees 
                                
                            
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                on Dec 20, 2021 3:55 PM
            
            
					
    
	
    

		
		
    
					
    Hi Jason,
    

    The VLED, or the LED anode voltage, is determined by the the forward voltage of the LED and the compliance voltage of the LED drivers LEDXx (refer to Figure 12 and Figure 13 on page #17 of the ADPD1080-1081 datasheet). The LED drivers, LEDXx, are current sink. When the LED driver LEDXx is off, the voltage at the LEDXx pin is at VLED subtracting the LED turn-on voltage; hence, the VLED shall be less the the sum of LED turn-on voltage and the 3.6V maximum rating of the LED driver LEDXx to GND. For a typical green LEDs with turn-on voltage of ~2.5V, the VLED can be as high as 6V. For red/IR LEDs, the recommended VLED is typically <4V due to the relatively low turn-on voltage.
    

    There is no integrated protection diode in ADPD1081. You can add an external protection for the LEDXx pin if you concern short circuit of LED(s).
    

    Regards,
    

    Glen B.
    

     
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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